This invention relates to a filter suitable for use in a high-frequency band in a communication equipment, especially a mobile radiophone.
A conventional stripline resonator is illustrated in FIG. 16. Referring to FIG. 16, the conventional stripline resonator is described. A side surface 104 and a bottom surface 105 of a dielectric plate 101 are metallized or plated over the entire surfaces thereof. The metallized or plated side surface 104 and bottom surface 105 are electrically maintained at the ground potential. A stripline resonator 103 is formed on a top surface 102 of the dielectric plate 101. The stripline resonator 103 is connected at one end thereof to an input terminal 108. At an area on the top surface 102, said area being apart by a predetermined distance from an opposite end of the stripline resonator 103, a marginal portion 106 is formed in such a way that the marginal portion is plated in continuation with the side surface 104. The opposite end of the stripline resonator 103 is connected to the marginal portion 106 via a lumped-constant element such as a capacitor 107.
As a consequence, capacitance C is realized between the opposite end of the stripline resonator 103 and the side surface 104 which forms a ground electrode, whereby the stripline resonator 103 is equipped with an increased quality factor Q.